The objectives of our studiesare to investigate the immunological functions and molecular natue of th alien H-2 specificities which we have detected on primary spontaneous and transplantable reticulum cell sarcoma (RCS) of SJL/J (H-2s) mice. RCS have been shown to express public H-2K/D antigens which are cryptic on normal SJL/J cells by cellular, serological and immunochemical prcedures. Furthermore, RCS express hybrid Ia antigens coded for by he Ia (Ae Beta chain) and IE/C (E alpha chain) subregions which are not normally expressed on host SJL/J (H-2s) cells but are present onlymphocytes of other haplotypes. In this proposal, we plan to define the molecular nature of the cross-reactive H-2 antigens susingmonospecific and monoclonal antibodies in order to determine if they are associated with he H-2K or D molecules. We will also define the biochemical nature of te hybrid IE/C antigen and its relationship to hybrid Ia of other H-2d and H-2k haplotyps. 1D and 2D PAGE will e done andsupplemented by peptide mappings. The role of alien antigens of RCS in the stimulation of syngeneic lymphocytes will be examined by the use of various recombinant strains anf F1 hybrids as responder and stimulator cells. The nature of stimulating antigens will be investigated by examining the effec of monoclonal antibodies on the proliferative response in vitro. Furthermore, the role of passive transfer of anti-alien antibodies on the in vivo tumor growth will be analyzed.